Bacteriophage Lambda is an excellent model system for studying virion assembly for the large DNA viruses, including the herpes, pox and adenoviruses. These viruses assemble empty protein shells into which the viral chromosome is packaged. In addition, during DNA packaging of many lambdoid phages and the herpes viruses, long end-to-end polymers of viral DNA are cut at specific sites to generate unit-length molecules.Viral DNA is selected for packaging from a DNA pool that also includes host sequences. This recognition is governed by the interactions of viral packaging proteins with a set of protein binding sites on the viral DNA. How protein-DNA interactions orchestrate packaging is best understood for . We propose to further define these DNA-protein interactions, which have broad implications for virus DNA recognition. We also seek to understand the mechanism of an assembly catalyst that aids recognition steps.While the functioning of the viral DNA packaging enzyme, terminase, has been extensively studied, the role of the shell, especially the shell's portal vertex, has not. We propose experiments on the portal's role in packaging, and seek to define the portal's binding site for terminase. As part of this work we plan to examine the roles of several proteins involved in shell assembly. This work will generate purified packaging proteins and assemblages suitable for structural analysis. Structural information about packaging proteins is crucial for understanding the wealth of genetic information and to assist in design of further studies on the functioning of these proteins.The mechanism of how DNA is translocated into the shell is not understood in any virus system. We propose molecular studies on a series of mutants that have defects in DNA packaging, including DNA translocation. We will also look at the ability of terminase to move DNA, and to pursue a structural analysis of functional domains of terminase.